A high-pressure capacitive pressure transducer is known in accord with U.S. Pat. No. 4,617,607, (the '607 patent) issued 14 Oct. 1986 to Kyong M. Park (who is a coinventor of the present invention) and Hung-Chih Chen, and which is assigned to the assignee of the present application. According to the teaching of the '607 patent, a high pressure transducer may include a high pressure fitting cooperating with a capacitive sensor module. The high pressure fitting includes a flexible metal diaphragm sealingly separating the high pressure fluid from the sensor module. An electrical circuit of the sensor module provides an electrical signal in response to fluid pressure force transmitted to the module via the flexible metal diaphragm. Also, the transducer includes a power supply for the electrical circuit of the module. A housing of the transducer includes at one end thereof the high pressure fitting, and a cylindrical portion of the housing encloses the sensor module and the power supply. At its end opposite the high pressure fitting, the housing includes an electrical connector providing for connection of the electrical signal externally of the transducer.
The transducer according to the '607 patent is accurate, rugged, and reliable. It is applicable over a considerable pressure range. Unfortunately, the transducer according to the '607 patent is somewhat expensive to manufacture. The housing of this sensor is somewhat complex, its parts count is high, and manufacturing assembly is undesirably time consuming. Also, while this transducer might be used either as a gauge pressure or absolute pressure sensor, it does not provide for its use as a differential pressure sensor.
Another conventional pressure transducer is known in accord with the teaching of U.S. Pat. No. 4,425,799, (the '799 patent) issued 17 Jan. 1984, to Kyong M. Park, and also assigned to the assignee of the present application. According to the '799 patent, a differential pressure transducer includes a pressure fitting sealingly cooperating with a pressure sensor module to define a first chamber. The pressure fitting defines part of a housing for the transducer, and provides for admission of a first pressurized liquid to the first chamber. The pressure sensor module includes a diaphragm on one side bounding the first chamber, and on the other side bounding a second chamber. The housing and pressure sensor module cooperatively define a passage connecting the second chamber with a port. At the port, the housing defines a liquid reservoir, and provides for communication to the reservoir to a second pressurized liquid. A low-viscosity liquid fills the second chamber, the passage, and part of the liquid reservoir. A membrane in the liquid reservoir sealingly separates the second pressurized liquid from the low viscosity liquid while providing for transmission of liquid pressure from the former to the latter. As with the pressure transducer taught by the '607 patent, the transducer taught by the '799 patent includes an electronic circuit for converting capacitance changes of the sensor module into an electrical signal. An opening in the housing of the transducer according to the '799 patent provides for extension outwardly of electrical conductors carrying this signal.
While the differential pressure transducer of the '799 patent is also accurate, rugged, reliable, and provides for measurement of differential pressures, it does not provide for its use either as a gauge or absolute pressure sensor. The pressure transducer according to the '799 patent is lower in parts count than the sensor according to the '607 patent, but is nevertheless more expensive to manufacture than is desired.
In view of the above, a need exists for a versatile low cost electronic pressure sensor which can be used either as a gauge pressure sensor, or as a differential pressure sensor, which can be used over a wide range of pressures, which by substitution of pressure sensor modules of different configurations and types allows the same or substantially the same housing design to be used also for other pressure measurement tasks, which allows parts commonality among the several sensor configurations, and which has wide-ranging applicability to a variety of pressure sensing uses in addition to the versatility of applications allowed by its use in either gauge or differential-pressure mode. Also the low cost pressure transducer should be rugged, accurate, reliable, and low in parts count to facilitate low costs of manufacture and assembly. A desirable pressure transducer of the foregoing type should also facilitate its calibration during manufacture and provide good retention of this initial calibration so that subsequent recalibrations are not needed. The sensor should also provide for shielding of the sensor module and circuitry from radio frequency interference (RFI) as well as electromagnetic interference (EMI). Desirably, such a low cost versatile pressure transducer should also filter out power supply surges or pulses so that the electronic circuitry of the transducer is protected and is not damaged by such surges or impulses.